Thiocyanic acid

Thiocyanic acid[1]
Names
	Preferred IUPAC name Thiocyanic acid[2]
	Other names Hydrogen thiocyanate; Sulfocyanic acid[3]; Sulfocyanide;
Identifiers
CAS Number	463-56-9 ;
3D model (JSmol)	Interactive image;
3DMet	B00344;
ChEBI	CHEBI:29200 ;
ChEMBL	ChEMBL84336 ;
ChemSpider	760 ;
ECHA InfoCard	100.006.672
EC Number	207-337-4;
Gmelin Reference	25178
KEGG	C01755 ;
MeSH	thiocyanic+acid
PubChem CID	781;
UNII	A5KWW7N91V ;
CompTox Dashboard (EPA)	DTXSID7047221 ;
	InChI InChI=1S/CHNS/c2-1-3/h3H Key: ZMZDMBWJUHKJPS-UHFFFAOYSA-N ;
	SMILES SC#N;
Properties
Chemical formula	CHNS
Molar mass	59.09 g·mol−1
Appearance	colorless, oily liquid
Odor	pungent
Density	2.04 g/cm3
Melting point	5 °C (41 °F; 278 K)
Solubility in water	Miscible
Solubility	soluble in ethanol, diethyl ether
log P	0.429
Acidity (pKa)	0.926
Basicity (pKb)	13.071
Hazards
	GHS labelling:
Pictograms
Signal word	Warning
Hazard statements	H302, H312, H332, H412
Precautionary statements	P261, P264, P270, P271, P273, P280, P301+P312, P302+P352, P304+P312, P304+P340, P312, P322, P330, P363, P501
Related compounds
Related alkanenitriles	Hydrogen cyanide; Cyanogen iodide; Cyanogen bromide; Cyanogen chloride; Cyanogen fluoride; Acetonitrile; Aminoacetonitrile; Glycolonitrile; Cyanogen;
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). verify (what is ?) Infobox references

Thiocyanic acid is a chemical compound with the formula HSCN and structure H−S−C≡N, which exists as a tautomer with isothiocyanic acid (H−N=C=S).[4] The iso- form tends to dominate with the material being about 95% isothiocyanic acid in the vapor phase.[5]

Tautomerism between thiocyanic acid (left) and isothiocyanic acid (right)

It is a moderately strong acid,[6] with a pK_a of 1.1 at 20 °C and extrapolated to zero ionic strength.[7]

HSCN is predicted to have a triple bond between carbon and nitrogen. It has been observed spectroscopically but has not been isolated as a pure substance.[8]

The salts and esters of thiocyanic acid are known as thiocyanates. The salts are composed of the thiocyanate ion (⁻SCN) and a suitable metal cation (e.g., potassium thiocyanate, KSCN). The esters of thiocyanic acid have the general structure R–SCN.

Isothiocyanic acid, HNCS, is a Lewis acid whose free energy, enthalpy and entropy changes for its 1:1 association with a variety of Lewis bases in carbon tetrachloride solution at 25 °C have been reported.[9] HNCS acceptor properties are discussed in the ECW model.

References

Merck Index, 11th Edition, 9257.
International Union of Pure and Applied Chemistry (2014). Nomenclature of Organic Chemistry: IUPAC Recommendations and Preferred Names 2013. The Royal Society of Chemistry. p. 784. doi:10.1039/9781849733069. ISBN 978-0-85404-182-4.
Richter, Victor von; Spielmann, Percy E., trans. (1922). Organic Chemistry or Chemistry of the Carbon Compounds. Vol. 1. Philadelphia, Pennsylvania, U.S.A.: P. Blakiston's Son & Co. p. 466.{{cite book}}: CS1 maint: multiple names: authors list (link)
Holleman, A. F.; Wiberg, E. (2001). Inorganic Chemistry. San Diego: Academic Press. ISBN 0-12-352651-5.
Beard, C. I.; Dailey, B. P. (1950). "The Structure and Dipole Moment of Isothiocyanic Acid" (PDF). The Journal of Chemical Physics. 18 (11): 1437. Bibcode:1950JChPh..18.1437B. doi:10.1063/1.1747507. hdl:1721.1/4934.
Munegumi, Toratane (23 January 2013). "Where is the Border Line between Strong Acids and Weak Acids?". World Journal of Chemical Education. 1 (1): 12–16.
Martell, A. E.; Smith, R. M.; Motelaitis, R. J. (2001). NIST Database 46. Gaithersburg, MD: National Institute of Standards and Technology.
Wierzejewska, M.; Mielke, Z. (2001). "Photolysis of Isothiocyanic Acid HNCS in Low-Temperature Matrices. Infrared Detection of HSCN and HSNC Isomers". Chemical Physics Letters. 349 (3–4): 227–234. Bibcode:2001CPL...349..227W. doi:10.1016/S0009-2614(01)01180-0.
. Barakat, T. M.; Nelson, J.; Nelson, S. M.; Pullin, A. D. E. (1969.) “Spectra and hydrogen-bonding of characteristics of thiocyanic acid. Part 4.—Association with weak proton acceptors”. Trans. Faraday Soc., 1969,65, 41-51

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[1] Merck Index, 11th Edition, 9257.

[2] International Union of Pure and Applied Chemistry (2014). Nomenclature of Organic Chemistry: IUPAC Recommendations and Preferred Names 2013. The Royal Society of Chemistry. p. 784. doi:10.1039/9781849733069. ISBN 978-0-85404-182-4.

[3] Richter, Victor von; Spielmann, Percy E., trans. (1922). Organic Chemistry or Chemistry of the Carbon Compounds. Vol. 1. Philadelphia, Pennsylvania, U.S.A.: P. Blakiston's Son & Co. p. 466.{{cite book}}: CS1 maint: multiple names: authors list (link)

[4] Holleman, A. F.; Wiberg, E. (2001). Inorganic Chemistry. San Diego: Academic Press. ISBN 0-12-352651-5.

[5] Beard, C. I.; Dailey, B. P. (1950). "The Structure and Dipole Moment of Isothiocyanic Acid" (PDF). The Journal of Chemical Physics. 18 (11): 1437. Bibcode:1950JChPh..18.1437B. doi:10.1063/1.1747507. hdl:1721.1/4934.

[6] Munegumi, Toratane (23 January 2013). "Where is the Border Line between Strong Acids and Weak Acids?". World Journal of Chemical Education. 1 (1): 12–16.

[7] Martell, A. E.; Smith, R. M.; Motelaitis, R. J. (2001). NIST Database 46. Gaithersburg, MD: National Institute of Standards and Technology.

[8] Wierzejewska, M.; Mielke, Z. (2001). "Photolysis of Isothiocyanic Acid HNCS in Low-Temperature Matrices. Infrared Detection of HSCN and HSNC Isomers". Chemical Physics Letters. 349 (3–4): 227–234. Bibcode:2001CPL...349..227W. doi:10.1016/S0009-2614(01)01180-0.

[9] . Barakat, T. M.; Nelson, J.; Nelson, S. M.; Pullin, A. D. E. (1969.) “Spectra and hydrogen-bonding of characteristics of thiocyanic acid. Part 4.—Association with weak proton acceptors”. Trans. Faraday Soc., 1969,65, 41-51